The present invention relates to hydraulic systems, and more specifically to a low pressure hydraulic system for an engine compression braking system.
Work machines commonly use hydraulic actuators, such as hydraulic motors and hydraulic pistons, as drive and operating mechanisms to perform work. A pressurizer, such as a pump or master cylinder supplies hydraulic fluid under pressure to the actuator. Hydraulic lines, which may be tubes, hoses, pipes or the like are used to interconnect the various devices in the hydraulic system, including the pressurizer and the actuator. For proper operation, the system, including all hydraulic lines, must be full of hydraulic fluid. In some machines, the hydraulic lines may be quite long, extending between devices. Long runs of hydraulic lines are often relatively straight, and are known to encompass drilled passages through metal bodies forming part of the work machine.
A known application for a hydraulic system is in the actuation of an engine compression brake. When required, the engine compression brake is actuated to open cylinder valves of the engine. The hydraulic system for an engine compression brake is known to include a bridge operating one or more engine cylinder valves, with movement of the bridge accomplished through the use of a hydraulic line circuit. A slave piston in the hydraulic circuit is connected to the bridge, and is moved in response to movement of a master piston also in the circuit. Passages drilled through the engine valve cover may be used to form part of the hydraulic fluid lines for the system. A sump and pressurized fluid supply are provided, with appropriate valves for effectively turning the hydraulic system on or off.
It is known to use multiple pistons in a hydraulic cylinder, including one or more floating pistons, for various purposes, including the operation of multiple branch circuits from a single master cylinder. U.S. Pat. No. 3,800,538 entitled, xe2x80x9cMaster Cylinders For Hydraulic Braking Systemsxe2x80x9d, discloses a master cylinder having a main first piston and two floating pistons collectively urged by a plurality of springs disposed in the cylinder.
A problem of hydraulic systems, particularly those operating at low pressures, is sponginess in response upon actuation of the system. This can occur due to the low bulk modulus of the hydraulic fluid at low pressures. Hydraulic systems used for engine compression brakes have been known to experience this type of problem.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, a hydraulic system is provided with a pressurizer for pressurizing hydraulic fluid, an actuator responsive to pressurized fluid to perform work and a hydraulic fluid line interconnecting the pressurizer and the actuator. A volume reducer in the hydraulic fluid line includes a substantially straight section of the hydraulic fluid line and a body slidable in the straight section in response to pressure changes in the hydraulic fluid line.
In another aspect of the invention, an engine compression braking system for an engine is provided with a cylinder valve, an actuator operating on the valve responsive to pressurized fluid, and a pressurizer for pressurizing hydraulic fluid. A hydraulic fluid line interconnects the pressurizer and the actuator. A volume reducer in the hydraulic fluid line includes a body slidable in the hydraulic fluid line in response to pressure changes in the hydraulic fluid line.
In still another aspect of the invention, a method for operating a hydraulic system with reduced hydraulic fluid volume is provided, with steps of providing a pressurizer for pressurizing hydraulic fluid and an actuator responsive to pressurized fluid to perform work; providing a hydraulic fluid line interconnecting the pressurizer and the actuator; providing a body in the hydraulic fluid line; pressurizing fluid in the hydraulic fluid line; and sliding the body in the hydraulic fluid line in response to pressure changes in the hydraulic fluid line.
In yet another aspect of the invention, a volume reducer for a hydraulic circuit is provided with a substantially straight hydraulic fluid line, and a body freely slidable in the hydraulic fluid line in response to pressure changes in the hydraulic fluid line.